The invention relates to expanding gate valves, and in particular, to expanding gate valves that have a position responsive interlock which controls the relative position of the gate and segment.
Heretofore, position responsive interlock assemblies have been utilized with an expanding gate valve to maintain the gate and segment in a collapsed position during travel between open and closed positions and to permit the gate and segment to expand at the open and closed positions of the gate valve assembly. Specific examples of earlier U.S. patents relating to gate valve interlocks are the U.S. Pat. No. 2,583,512 for a "Gate Valve" issued to Laurent on Jan. 22, 1952, the U.S. Pat. No. 2,855,175 for a "Gate Valve" issued to Dunbar on Oct. 7, 1958, and the U.S. Pat. No. 4,188,014 for "Gate Valve with Position Responsive Interlock" issued to Alvarez on Feb. 12, 1980.
Heretofore, the gate and segment have expanded from each other by movement through a pin-slot arrangement. Even though the movement through this arrangement was satisfactory, the stresses between the pin and slot acted on a relatively small area which resulted in galling of the pin and slot. This galling required the premature shutdown of the valve to perform the necessary maintenance. Thus, it would be highly desirable to provide an improved position responsive interlock assembly for use with an expanding gate valve wherein the galling of the pin and slot is reduced.
Earlier devices utilize seat skirts that have mediately disposed recesses and the like formed in their flanges. These recesses are generally formed by special manufacturing operations which result in increased production costs. Further, the removal of material to form these recesses reduces the strength of the flange along its length. Thus, it would be highly desirable to provide an improved position responsive interlock assembly for use with an expanding gate valve wherein the seat skirt thereof does not contain any specially formed recesses and the like thereby eliminating any special and generally relatively expensive manufacturing operations as well as providing a seat skirt that is of an optimum strength along its entire length.
In earlier devices, before the rocker arm can pivot into a locking position, it must overcome its tendency to pivot about the point where it engages the skirt. This tendency impedes the rocker arm from quickly moving into a locking position upon the displacement of the gate assembly from its expanded position. Thus, it would be highly desirable to provide an improved position responsive interlock assembly for use with an expanding valve wherein the rocker arm thereof more easily overcomes its tendency to pivot about the point where it engages the skirt.